The invention relates to a method of optimizing transmission, which method is used at a transmitter receiving several digital signals that are modulated, which transmitter comprises converter means converting a signal into an analog signal before signal transmission, and in which method the position of the signal to be converted within the dynamic range of the converter means affects optimality of the signal obtained from the conversion.
The invention also relates to a transmitter receiving digital signals, which transmitter is used in a radio system to optimally transmit signals, the transmitter comprising modulation means arranged to modulate the received signals, and converter means converting the digital signal into an analog signal before signal transmission, the position of the signal received by the converter means within the dynamic range of the converter means affecting optimality of the signal obtained from the conversion.
In prior art radio systems, such as GSM radio systems, a signal coming from the direction of a fixed network usually propagates to a base station via a mobile exchange and a base station controller. The base station operating as a transmitter receives a digital signal coming from the direction of a fixed PSTN network and forwards the signal to a subscriber terminal. Depending on the radio system used, the base station also has information on directing the signal to be transmitted into the desired timeslot, for example. In addition, the base station has information on the power level at which the signal is transmitted, for example. Generally, the base station transmits signals to subscriber terminals at different power levels according to instructions obtainable from the radio system. When transmitting the signal, the base station operates as a transmitter.
The base station performs various types of codings, such as channel coding, to data comprising the received signal, after which digital signals coming from different channels are modulated. After the modulation, the signals are converted into analog signals, after which the signals are combined in the analog parts of the transmitter. Next, the combined signal is amplified and transmitted onto a radio path.
The spectrum of a signal transmitted by a prior art transmitter, such as a base station, comprises various types of interference caused by the conversion of digital signals into analog signals and by the combining of the signals. The base station receives signals whose frequencies and power levels are usually very different. Problems are particularly caused by signals coming to a DIA converter at different power levels, since, in prior art solutions, constant optimal utilization of the dynamic range of the converter is impossible. In addition, converters available at the moment cannot tolerate interference in the signal well enough. After the combination, the signals with different power levels also bring about interference, particularly to adjacent channels.
EP 735 702 discloses a signal reception method employing the weighting of the received signal. However, the method disclosed in the prior art differs from the one disclosed in the application, for example, in that in the method disclosed in the prior art, signals are not set into a correct mutual relation after they are combined and converted into analog signals. In addition, the method disclosed in the prior art is used in signal reception, whereas the one disclosed in the application is used at a transmitter.
EP 263 357 discloses a reception method in which signals are received with several antennas. The received signals are combined by using weighting coefficients. The method disclosed in the prior art is used in signal reception, whereas the one disclosed in the application is used at a transmitter. Furthermore, in the method disclosed in the prior art, the manner of weighting the signal differs from the one in the method disclosed in the application.
EP 807 988 discloses a method of generating weighting coefficients. The disclosed method differs from the one disclosed in the application in that in the method disclosed in the prior art, no reference is made to combining the weighted signal and converting the combined signal into an analog signal, for example.
The method disclosed in EP 806 844 differs from the one disclosed in the application in that it is used at a receiver. The method disclosed in the prior art uses weighting coefficients, but the weighting coefficients are feed-back-controlled.
JP 921 9615 discloses a transceiver structure using a reference signal for calculating weighting coefficients. In addition, adaptive antenna arrays are used at the transceiver. It is not necessary to use antenna arrays in the solution of the application. In addition, a reference signal as disclosed in the prior art is not used in the method disclosed in the application.
An object of the invention is to provide a method and transmitter to solve the above problems. This is achieved by a method of the type presented in the introduction, which is characterized in that each modulated signal is weighted by a specific weighting coefficient so as to set the mutual power levels of the signals into predetermined relations and to optimally dispose the signals within the dynamic range of the converter means, the signals are combined after the weighting, and the combined signal is converted into an analog signal, after which the combined signal is scaled to a predetermined power level.
The transmitter is characterized in that it comprises means for generating weighting coefficients, means for weighting each modulated signal by a specific weighting coefficient so as to set the mutual power levels of the signals into predetermined relations and to optimally dispose the signals within the dynamic range of the converter means, means for combining the weighted signals, after which the means convert the combined signal into an analog signal, and means for scaling the signal converted into the analog signal to a predetermined power level.
The preferred embodiments of the invention are disclosed in the dependent claims.
The invention is based on the idea that a signal coming to a DIA converter is so processed that after the processing, the signal utilizes the dynamic range of the converter as optimally as possible. In the solution of the invention, the dynamics the D/A converter is optimized when several digitally modulated signals are combined. This is done in two phases. In a first phase, the power levels of the signals are set into a correct relation with one another in such a way that the dynamics of the converter becomes optimally utilized. The modulated signals are combined, after which the combined signal is set to the absolutely correct power level.
The method and transmitter of the invention provide many advantages. The method enables conversion of digital signals at different power levels into analog signals in such a way that a signal coming to the transmitter even at a very low power level is converted by optimally utilizing the dynamic range of a converter. This is implemented in such a way that each received signal is weighted by a weighting coefficient matched to the signal, whereby the word length of the signal can be matched to the maximum word length of the converter, and problems caused by different signal power levels are thus solved. The transmitter can be implemented with fewer analog parts or by combining analog parts, whereby the transmitter can be implemented at a lower cost. In addition, the transmitter tolerates interference much better than previously implemented transmitters. Furthermore, the transmitter of the invention consumes less power than prior art transmitters, since the number of analog parts consuming power can be reduced, for example.